The invention lies in the field of chromatic confocal measurement technology and image sensors having an extended depth of field range.
A measuring device of the generic type comprises a light source, which emits light of a plurality of wavelengths, wherein a measurement object is illuminated by means of the light source. Moreover, this comprises a first beam splitter, via which the light from the light source is guided into an imaging optical unit, wherein the imaging optical unit has a pronounced chromatic aberration. Light reflected from the measurement object is imaged by the imaging optical unit and the first beam splitter onto a first confocal detection stop arrangement, in such a way that the first confocal detection stop arrangement functions as a confocal aperture. Advantageously, light both reflected directionally from the surface and reflected diffusely from the surface is detected. A first detection device detects light incident through the first confocal detection stop arrangement and evaluates it.
EP 3 222 964 A1 discloses a chromatic confocal device for determining the surface of an object. The device comprises a broadband light source and a lens having chromatic aberration, such that light of different wavelengths is focused at different axial distances. The device comprises a plurality of optical measurement channels that respectively image a point on the object surface, wherein a total intensity over all wavelengths is evaluated, instead of a spectral evaluation, at least for a portion of the measurement channels. In one embodiment of the device, the output channels are formed by optical fibers with fiber couplers, such that the total intensity and the spectrum of a measurement channel can be evaluated simultaneously. On the illumination side, the light from the light source is likewise guided by optical fibers, wherein the fiber ends serve as confocal measurement or illumination apertures and are imaged by the device onto the measurement points on the object.
Said device has the disadvantage, however, that, owing to the individual fibers, continuously uniform illumination and imaging of the object is not possible. Moreover, with the use of fibers, the diameter and spacing of the measurement points are limited by the diameter of the fibers which form the measurement channels. In the case where the desired measurement point spacings and diameters are significantly less than the diameters and spacings of the fibers, an objective lens having a reduction scale beta <<1 is required, which significantly increases the costs and the dimensions for the objective lens. The ratio of fiber core to fiber external diameter additionally imposes a lower limit for the ratio of point diameter to point spacing. If the measurement point spacings and diameters are intended to be variable, then movable parts of the objective lens are required, as a result of which the costs and dimensions increase still further. If the fibers are omitted, then it is no longer possible for the total intensity and the spectrum to be evaluated simultaneously (paragraph 131 of EP 3 222 964 A1). A large number of fibers and fiber couplers that would be required to measure a large spatial region all at once are moreover very expensive and voluminous.